US2240019A

US2240019A - Method of making and cooling tubes

Info

Publication number: US2240019A
Application number: US236364A
Authority: US
Inventors: Bert L Quarnstrom; Raymond H Hobrock
Original assignee: Bundy Tubing Co
Current assignee: Bundy Tubing Co
Priority date: 1938-10-21
Filing date: 1938-10-21
Publication date: 1941-04-29
Anticipated expiration: 1958-04-29

Description

Apn'l 29 1941. B. 1 QUAN'sTRoM E11-AL. 2,240,019

` UETHOD 0F MAKING AND COOLING TUBES Filed Oct. 21, 1938 2 Sheets-Sheet 1 20:02. ZOOmw .H12 mZON AN .mZON Hm. U 5 o fm MZON m m m c m O 0 O r nl n @m3 HH A M mu, Y n L 0 ummm* n bv nu BR .N .www m wa@ enum ...m o 25 nw www Em zubo .uw

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.QH mE April29, 1941. B. l.. QUARNSTROM E'r-AL 2,240,019

u ETHOD QF MAKING AND COOLING TUBES 2 Sheets-Sheet 2 Filed loat. 21,1952',

IIII .Illll of of QN:

, Patente pr.. 29, '194i urrE ANT Price? 2,240,019 1 l Murnon or mmc am cootnvc 'runes Bert lL. Quarnstrom and Raymond H. Hiobrock,

hetroit, Mich., assignors to Bundy Tubing Company, Detroit, Mich.,a corporation of Michigan Application @ctobcr 21, 1938, Serial N0. 236,364

d Claims.

and it has to ldo particularly with the making of tube fashioned from stripsteel stock and sealed with a high melting point sealing metal such as copper, cuprous alloys or other so-called hard solder.

The invention is directed particularly to the.

. of tube where the tube moves at lower speeds.

To state with clearness what is meant by relatively great speed 01 movement, it is pointed out,

' by way of example, that such a speed is in the vicinity of 100 feet per minute and may be as great as,.or greater, than about 150 feet per minute. This is an example only, but serves to point out the invention with deniteness.

` It will be appreciated that it is usually preferred to have small size tubing, which is used (El. la-21.5) This invention relates to the making of tube,`

emplify the invention, it will be described primalrily with reference' to production of relatively ductile tube. To this end, the cooler is so arranged that successive sections of the tube are cooled in different zones or steps and at diderent rates. Throughout some temperature ranges, rapid cooling may take place with no deleterious effect, and in such temperature ranges the tube is relatively'rapidly cooled:l Throughout other temperature ranges where rapid cooling results in hardness or brittleness, the tube is cooled less rapidly. The cooler is so organized that the suc-` cessive cooling zones or steps act upon the continuously moving tube,'with successive sections of the tube moving respectively through the different zones.

The invention is admirably adapted for use Y with a tube making apparatus which employs in automobiles for gasoline lines, oil lines, hy-

draulic brake lines or the like,l and tubing used in condensers or evaporators for refrigeration, or other heat exchange devices, in a relatively ductile condition. This is desirous for a number of reasons and also such tube can be easily shaped or handled. Where such a tube is made with a relatively high rate of longitudinal movement, and is elevated to a high temperature, a cooler for cooling the tube at such a slow rate as to obtain requisite ductility would have to be so long as to be impracticable. On the other hand, if the cooler is shortened to a practicable length, and the steel is cooled too rapidly, the steel of the finished tube will be undesirably hard and brittle.

It is the aim of this invention to provide an' improved arrangement for cooling tube made from strip steel stock and which, invits making,.

is subjected to a high temperatureand which moves at a relatively high rate of speed, wherein the cooling action is so organized and zoned that the length of the cooler may be reduced to a. prac' ticable length, while at the same time the metal is given the desired ductile characteristic. As a matter of fact, the characteristic of the metal may be variably controlled; but in order to exelectrical resistance for the heat treatment of the tube; that is to say, electric current is passed through successive sections of the tube for heating it,` and with this arrangement, the high speed of or 150 feet per minute may be obtained.

`The invention is exemplified in the accompanying drawings wherein Fig. 1A is a diagrammatic illustration of a tube 4mill and heating means for the tube.

Fig. 1B is an illustration, of a diagrammatic nature, showing the cooling apparatus.

Fig. 2 depicts a temperature curve, showing'the cooling of the tube in the several zones of the cooling structure shown in Fig. 1B.

Fig. 3 is a View showing a modified form of cooling apparatus.

Fig. 4 shows a temperature curve of the cooling structure shown in Fig. 3.

Fig. 5 is a view of a still further modified form of cooling apparatus.

Fig. 6 is a cross sectional View of one form of tube which may be made.

A strip of steel stock l. forms the inner ply of the finished tube as shown in Fig. 6, and a strip of stock 2 forms the outer ply. 'Ihe strip l may be drawn from a supply reel 3 and moved through a plurality of forming rolls of a tube mill generally illustrated at 4 and fashioned into tubular form as shown in Fig. 6. In the form of tube shown the edges of the strip l are arranged in a ply and strip 2 are passed through a plurality of' rolls of a tube mill generally illustrated at .those versed in the art which .fashion the strip 2 into tubular form around the inner ply, the edges coming together in a scaried seam as shown in Fig. 6. This exastenia emplifies one way of making a tube which may be treated in accordance with the present invention,

and need not be further described in detail. Tube mills are also known for fashioning tube from a single strip having eithera single ply or double ply.

The tube thus formed is subjected to heat treatment to melt a sealing metal which, upon solidication, unites the plies and the seams. rlrhis sealing metal may be supplied in the form of a coating on one or both of the strips. The strip l or the strip 2, or both, may be coated or plated on one or both sides with the sealing metal. Upon the heating of the tube above the sealing metal melting temperature, the sealing metal is rendered molten, and upon solidication seals the tube by uniting the overlapping and juxtapositioned parts. the tube mill may bel driven for the purpose of propelling the strip and tube with longitudinal movement.

The tube may be heated by electrical resistance in a manner illustrated in Fig. 1A wherein a pair of electrodes i2 and electrodes it and it engage the tube. A transformer for alternating current is generally illustrated at i5 and the outside electrodes l2 and id are connected to one side of the secondary by leads i6 and. i'i, while the and tube mills of this nature are known to substantially from the rollers 2T lor the housing containing the rollers to the dividing partitions t2. The second cooling zone is also shown as a water jacketed arrangement having an outer water jacket 3! with the water being circulated therethrough and entering at 35 and leaving at it. A cooling gas may also be circulated in direct contact with the tube` by entering the cooling zone at ti and passing out at 38.

The second cooling zone is shown terminating at the partition arrangement dt. The rst section of the third cooling zone is illustrated as an air cooled arrangement having heat radiating fins lll and terminating at the partitioning arrangement Il?. This illustration is not intended to limit these zones to the precise type of cooling arrangement shown, since the first section of the third cooling zone may be water jacketed or may f. have gas introduced therein, and the iirst and `Sonie oi the rollers of intermediate electrode iti is connected to the other side of the secondary by a lead it. With this arrangement there is no potential across electrodes l2 and it. Accordingly, current flows through successive sections oi the tube between electrodes l2 and it and between electrodes i3 and ifi.

With this arrangement it is feasible to bring the tube up to the desired temperature between electrodes IZ and i3, and to maintain the teinperatui'e between electrodes i3 and ii. This, however, is claimed in application Serial Number 229,015, filed September 8, 1938.

Where desires or conditions dictate, the tube may be maintained in a non-oxidizing or reducing environment while in its heated condition. To this end, the electrodes and 'tube may be enclosed by a housing structure indicated at 2t and anon-oxidizing or reducing gas may be passed into the housing through an inlet 2 i The gases may burn on at the entering end 22 and at a burn-oit pipe 23.

'Il'he structure shown in Fig. `1li is to be placed in alignment with the structure shown in Fig. 1A so that the tube moves directly from the tube Vmill and heating apparatus of Fig. 1A into the cooling structure shown in Fig. 1B. The housing 20 may connect the two structures as indicated, and a pair of rolls, which may be for guiding or propelling the tube, is illustrated at 25 and may be disposed in a housing-2t` connected to the housing 2G.

-It is thought best to rst describe in a general manner, the several cooling zones, and then to follow the general description with a more detailed explanation. The iirst zone is diagrammatically depicted as a water-jacketed structure having an outer water-jacket structure 2l with the water entering the pipe 28 and leaving through pipe 29. A cooling gas may be circulated in direct contact with the tube, the gas entering through a pipe 3u and passing out through pipe 3l. The first cooling zoneextends second zones may likewise embody different cooling arrangements.

The second section of the third cooling zone is shown in the form of a liquid cooling or quench ing arrangement, and comprises a tubular hous-52 ing dil surrounding the tube. Molten metal such as a molten lead or a molten lead and tin alloy or other similar metal, or molten salt, is prei= erably moved in a circuitous path by suitable pumping means, and is pumped into the housing i3 through the pipe it and is discharged at opposite ends thereof through pipes i5 and git. Any suitable pumping means may be used. Where it 'is desired to have the nished tube coated with lead or tin, or an alloy of lead and tin, or other metal, such molten metal may be used in the second section of the third Zone. Where no coating is desired molten salt may be employed. As the tube passes out of the second section of the third zone, it may be passed through a wiping device d1, wiping on the excess coating metal received in the chamber fit? or for wiping. oii' the salt, and then the tube may be finally cooled by introducing it to the atmosphere or by means of a Water spray de. A hot water spray (not shown) may also be used for removing the last vestiges of salt.

Where steel strip is used for forming the tube and the strip is sealed by copper, it is preferred that the temperature to which the tube is subjected is considerably in excess of copper melting temperature. This tempertaure may be in the vicinity of 2200 F., as illustrated in Fig. 2. Ordinarily,'with low carbon steel, the carbon exists as a constituent known as cementite usually surrounded by grains of iron called ferrite. If the steel, however, is elevated to a temperature. in excess of the upper critical temperature, say 1670 F., the carbon dissolves in the crystal form of gamma iron to form a constituent known as austenite. The austenite constituent maintains at temperatures above the upper critical, but upon cooling through the transformation range, namely, from the upper critical, as for example 1670 F. to 330 F., the austenite transforms to a type ofdispersion of cementite in the alpha iron.

Since there is4 no'tendency for the austenite to transform at temperatures above the critical temperature, the tube is cooled rapidly from its 4 @,Mi the tube through the transformation temperature range at a relatively reduced rate of speed in order to allow sumcient time for the transformation of the austenite to the desired phases or structures in the alpha iron, such as the socalled cementite. Unless the austenite is given an opportunity to transform, the resultant metal may be hard and brittle. Therefore, in order to produce av ductile tube, the second zone is arranged to cool the metal through the transformation range with such slowness as to facilitate the desired ductility. However, the second zone maybe arranged to cool the tube to obtain any desired characteristics in the metal.

Moreover, it is desired that the cooling rate through the second zone be relatively constant. The tube enters the second zone at a higher temperature than it leaves the second zone and,

accordingly, there would normally be a greater temperature gradient and a resultant more rapid cooling in the early stages of the second zone than in the later stages of the second zone. To meet this Y situation the cooling gases may be caused to enter the second cooling zone near the outlet end. These gases are heated in the action of cooling the tube near the outlet end and then move toward the inlet end of the second zone with the result that the temperature gradient throughout the second zone may be made relatively uniform.

`After the tube is passed through the second zone, the ferrous metal is in the form known as alpha iron, and the austenite has been transformed so as to approach a condition of equilibrium in the alpha iron. However, the solubility of carbon in alpha iron is greater at higher temperatures than at lower temperatures. Accordingly, if the alpha iron is cooled too rapidly in the third zone, and particularly in the rst section of the third zone, a condition of super-saturation will result at room temperature. Under these conditions a phenomenon known as aging may be detected in an increase in the hardness of the metal, a decrease of ductility, an increase in ultimate strength and an increase in brittleness. Thus aging of this kind results in a steady decline in a number of the desirable features of the metal in the course of time.

The cooling in the third zone is arranged to overcome this objection. One way is to avoid the supersaturation. In Fig. Z, the iirst section of the third zone cools the metal relatively slowly down to about l000 F., and thus great supersaturation can be avoided, and such small supersaturation and the resulting aging whichmi'ght occur will be entirely dependent upon the small change in solubility between 1000 F. and room temperature; but from 1000 F. downwardly@ there is not so much of a change. Another way is to set up an aging action, as will be later dis cussed with reference to Figs. 3 and d.'

The second section of the third zonemay be arranged to cool the tubemore rapidly but still preferably less rapid than the final cooling. Where the tube is to be coated with metal, a molten metal such as one of the metals above mentioned may be circulated through the second section of the third zone, and'this is preferably arranged to lower the temperature of the tube to about 600 F. In any event, the tube is cooled to a temperature low enough to prevent rapid Subsequently, the tube may be passed to the atmosphere and excess molten metal or salt may be removed by wiping means, and then the tube nally cooled either by the atmosphere or by a water spray.

In Fig. 3 a modified arrangement is shown. The rst zone performs the same function as the rst Zone shown in Fig. 1B namely, a rapid cooling of the metal down to the upper critical temperature.V The second zone is also designed to perform the same function as the second zone shown in Fig. 1B, namely, that of slowly cooling the metal through the transformation temperature range. The third zone, as distinguished from a zone for preventing supersaturation, is designed to first rapidly cool the alpha iron to set up an unstable condition, and then to allow a period of time for aging at high temperatures,

at 5i and removed at 52 and 53, the molten metal or salt being circulated through the third zone chamber. This cools the tube rapidly as shown by the corresponding temperature curve in Fig.

4, and then maintains this relatively high temperature for a period of' time, as indicated, to

allow for the aging action at high temperatures.

The aging action at relatively high temperature is, ofcourse, much more rapid than at room temperature. As illustrated, this third zone quickly lowers the temperature to about 700 F. and then this is maintained for a period of time whereupon the tube is passed out of the cooling apparatus into the wiper and water spray as above described. In Fig. 3, the reference characters applied to the rst and second zones and to the final wiper and water spray are the same as those used inthe form shown in. Fig. 1B. This third zone may cool the tube downto any desired temperature for the aging period; for example, the aging temperature may be from about 700 F. to 900 F.

In Fig. 5 a still further modied arrangement is shown wherein the irst, second and third cooling zones correspond to the ooolingzones shown in Fig. 3, and the same reference characters are applied. However, as illustrated by the curve in Fig. 4, the Eg. 3 form may pass the tube into the atmosphere at too high a temperature, resulting in rapid discoloration or oxidation and also resulting in some supersaturation at room. temperature. In Fig. 5 an additional cooling section 55 may be employed, the same being shown in the form of a quenching unit, into which a suitable cooling liquid may be introduced and circulated through pipes 5t' and 5l. This liquid may also be a molten liquid or salt but maintained at a temperature lowe'r than `the metal or salt in `the third zone. The temperature curve for this form throughout the first, second and third zones is shown in Fig. 4, and is the same as the temperature curve for the form shown in Fig. 3. However, the temperature curve for the final or fourth zone of cooling is shown by the dotted lines in Fig. lwherein it will be noted that the temperature of- 'the tube is dropped to aboutv 600F. or lower more slowly, passed to the atmosphere.

Accordingly, it will be observed that the cooling of the tube from a point above the upper critical temperature to a temperature at which the tube may be passed into the atmosphere is divided into l.and then is nally j i anaemia zones. Throughout such temperature 'ranges where rapid cooling produces no deleterious results the tube is cooled rapidly; throughout other temperature ranges where rapid cooling `would produce deleterious effects, the tube is cooled relatively slowly. In one form, however, namely, the forms shown in Figs. 3 and 5, the tube is cooled rapidly from a point below the lower critical, which results in the setting upl of a supersaturated condition, and then the tube is maintained at a relatively high temperature for a period of time resulting in a high temperature aging. The net result is an over-all reduction of the-.length of the'cooling apparatus. Also, the

characteristics of the metal of the nished product can be determined and controlled. For example, if a very hard brittle structure is desired, the second zone may be arranged so as to maintain some transitional structur such as martens ite in the metal when it is cooled. 0n the other hand, the third zone may be arranged to act as a tempering or drawing zone in which the struc` ture produced by the relatively rapid cooling in the second zone is tempered or modified so that the desired characteristics may be obtained in the @nished product.

We claim:

1. In the method of making a. ductile tube from' strip carbon steel stock wherein the strip is fashioned into tube while the strip and the tube formed therefrom move longitudinally atv a rate of speed in the vicinity of 100 feet per minute and upwards and wherein the entire tube is heated to a temperature above the transformation temperature of the steel and above 2000 Fffor the uniting of' juxtapositioned parts of the strip stock, the steps of cooling the moving tube which comprises, cooling the tube relatively rapidly throughout the temperature range above substantially the upper transformation temperature,

cooling the tube throughout the range between substantially the upper and lower transformation temperatures relatively slowly and at such a rate and through a time period that the austenite transforms substantially into a type of dispersion of cementite in alpha iron, then cooling the tube substantially from the lower transformation tempersion. of cementite in alpha iron,

tion temperatures relatively slowly and at such a rate and through a time period that the austenite transforms substantially into a type of disand then cooling the tube substantially from the'lower transformation temperature to a temperature where the tube may be passed to the atmosphere. at a rate so that the decreasing solubility of carbon in the cooling iron does not exceed substantially the rate of precipitation and coagulation of the carbon in the alpha iron to prevent a super-saturationv condition all with continuous movement vof the tube.

3. lin the method of making a ductile tube from strip carbon steel stock wherein the strip is fash ioned into tube while the strip and the tube formed therefrom `move longitudinally at a rate of speed in the vicinity of 10() feet per second and upwards and wherein the entire tube is heated to a temperature of about 2200" F. for the uniting of juxtapositioned parts. of the strip stock, the steps of cooling the moving tube which comprises cooling the tube relatively rapidly down to substantially the upper transformation temperature, cooling the tube throughout the range between substantially the upper and lower transformation temperatures relatively slowly and at such a rate end through a time period that the -austenite substantially transforms into a type ofv dispersion of cementite in alpha iron, cooling the tube from substantially the lower transformation temperature down to about 1000o F. through a time vperiod and rate as to subsaturation of the dispersion of cementite in alpha f iron, and then relatively rapidly further cooling perature to a temperature where the tube may be passed to the atmosphere and through a time period such that when the tube is passed to the atmosphere there is substantially no objectionable supersaturation of cementite in alpha iron all with continuous movement of the tube.

. 2. In the method of making a ductile tube from strip carbon steel stock wherein the strip is fashioned into tube while the strip and the tube formed therefrom move longitudinally at a rate of speed in the vicinity of 100 feet per second and upwards and wherein the entire tube is heated to a temperature of about 2000 F. for the uniting of juxtapositioned parts of the strip stock, the steps of Prises.

throughout the temperature range above substantially the upper transformation temperature, cooling the tube throughout the range between substantially the upper and lower transformacooling the 'moving tube which comcooling the tube relatively rapidly the tube for passage to the atmosphere.

d. In the method of making a ductile tube from strip carbon steel stock wherein the strip is fashioned into tube while the strip and the tube formed therefrom move longitudinally at a rate of speed in the vicinity'of 100 feet per minute and upwards and wherein the entire tube is heated to a temperature substantially above the transformation temperature of the steel for the uniting of juxtapositioned parts of the strip stock, the steps of cooling the moving tube which comprises cooling the tube relatively rapidly down to substantially the upper transformation temperature, cooling the tube throughout the range between substantially the upper and lower transformation temperatures relatively slowly and at such a rate and through a time periodv that the austenite substantially transforms into a type of dispersion of cementite in alpha iron, relatively rapidly cooling the tube substantially from the lower transformation temperature to a temperature of about 700 F. or above, maintaining said last named temperature for a period of time for effecting a high temperature'aging to l substantially eliminate supersaturation of ce-v